The invention relates to a loading crane that can be attached to a truck and that has a boom including several telescopic arms, wherein one hydraulic unit, comprising piston and cylinder, it arranged between each pair of successive arms. Upon telescoping an arm, a stop attached to the preceding arm actuates a valve which is moved along with the telescoped arm and which releases the hydraulic supply for the subsequent arm.
Sequence controls for loading cranes have the purpose of ensuring that the individual arms of a telescopic boom are telescoped or retracted in a specific, usually fixed order of sequence. This is achieved either by means of an electro-hydraulic controller (DE-PS 26 48 608) or by avoiding electric components with significant mechanical complexity (DE-OS 34 13 443). Correspondingly, the loading cranes used in the past by the Palfinger Aktiengesellschaft company are equipped with a mechanically simple sequence control of the type defined above and which has, however, the drawback that only that arm of the telescopic boom that is braced directly against the folding arm enveloping the preceding arm is automatically telescoped first. The other parts of the telescopic boom are, in contrast, not fixed with respect to the order of sequence at which they are telescoped.
In the case of the cranes, in prior public use, of the Palfinger Aktiengesellschaft, the valve which is actuated by means of the stop attached to the folding arm is on the piston-sided end of the hydraulic cylinder that actuates the first arm, such end being directed toward the folding arm. Not until this first arm is totally telescoped does the valve designed as a non-return valve release the throughflow of hydraulic fluid to the cylinders of the other telescopic arms.